System and process for generating electrical power

Abstract

The present invention relates to a process for generating electricity with a solid oxide fuel cell system with low carbon dioxide production. First and second gas streams containing hydrogen are fed at independently selected rates to an anode of a solid oxide fuel cell. The first and second gas streams are mixed with an oxidant at one or more anode electrodes of the solid oxide fuel cell to generate electricity. An anode exhaust stream comprising hydrogen and water is separated from the anode of the fuel cell, and the second gas stream comprising hydrogen is separated from the anode exhaust stream and fed back to the anode of the fuel cell. The rates that the first and second gas streams are fed to the fuel cell are selected so the fuel cell generates a high electrical power density. Recycle of the hydrogen from the anode exhaust reduces the amount of hydrogen required to be generated to operate the fuel cell, thereby reducing the carbon dioxide produced in the generation of hydrogen required to operate the fuel cell.

1 . A process for generating electricity, comprising:
 generating a first gas stream containing hydrogen from a feed containing one or more hydrocarbons;   feeding the first gas stream at a selected rate to an anode of a solid oxide fuel cell;   feeding a second gas stream containing hydrogen at a selected rate to the anode of the solid oxide fuel cell;   in the anode, mixing the first gas stream and the second gas stream with an oxidant at one or more anode electrodes of the solid oxide fuel cell to generate electricity at an electrical power density of at least about 0.4 W/cm 2 ;   separating an anode exhaust stream comprising hydrogen and water from the anode of the solid oxide fuel cell; and   separating the second gas stream from the anode exhaust stream, said second gas stream comprising hydrogen separated from the anode exhaust stream;   wherein carbon dioxide is generated at a rate of no more than about 400 g per kWh of electricity generated.   
   
   
       2 . The process of  claim 1 , wherein the first gas stream and the second gas stream are fed to the anode at selected rates effective to generate electricity at an electrical power density of at least about 0.5 W/cm 2 . 
   
   
       3 . The process of  claim 1  wherein carbon dioxide is generated at a rate of at most about 350 g per kWh of electricity generated. 
   
   
       4 . The process of  claim 1  wherein separation conditions are selected for separating the first gas stream from the reformed product gas to provide a first gas stream containing at least about 0.7 mole fraction hydrogen. 
   
   
       5 . The process of  claim 1  wherein separation conditions are selected for separating the first gas stream from the reformed product gas to provide a first gas stream containing at most about 0.15 mole fraction carbon oxides. 
   
   
       6 . The process of  claim 1  wherein separation conditions are selected for separating the second gas stream from the anode exhaust stream to provide a second gas stream comprising at least about 0.9 mole fraction hydrogen. 
   
   
       7 . The process of  claim 1  wherein the rates that the first gas stream and the second gas stream are fed to the anode are independently selected so the ratio of the amount of water formed in the fuel cell to the amount of hydrogen in the anode exhaust stream is at most about 1. 
   
   
       8 . The process of  claim 1  wherein the rates that the first gas stream and the second gas stream are fed to the anode are independently selected so the anode exhaust stream contains at least about 0.6 mole fraction hydrogen. 
   
   
       9 . The process for generating electricity of  claim 1  wherein the first gas stream is generated by steam reforming a feed comprising one or more hydrocarbons. 
   
   
       10 . The process for generating electricity of  claim 1  wherein the first gas stream is generated by partially oxidizing a feed comprising one or more hydrocarbons. 
   
   
       11 . The process for generating electricity of  claim 1  wherein the first gas stream is generated by steam reforming a feed comprising one or more hydrocarbons to form a reformed product gas and separating the first gas stream from the reformed product gas. 
   
   
       12 . The process for generating electricity of  claim 1  wherein the first gas stream is generated by partially oxidizing a feed comprising one or more hydrocarbons to form a product gas and separating the first gas stream from the product gas.